A twin-engine helicopter is equipped with two turboshaft engines which operate in regimes which are dependent on the flight conditions of the helicopter. It is known that a twin-engine helicopter can have two main regimes, a regime known by the abbreviation AEO (all engines operative) in which the two turboshaft engines operate normally in predetermined regimes, and a regime known by the abbreviation OEI (one engine inoperative) in which one of the turboshaft engines is inoperative. This OEI regime occurs following the loss of one engine. When this event occurs, it is necessary for the good engine to accelerate rapidly so that it can provide the maximum permissible power thereof in an emergency situation and thus make it possible for the helicopter to cope with the perilous situation, then to be able to continue the flight.
Throughout the following text, the malfunctioning turboshaft engine will be referred to by the term “inoperative turboshaft engine” and the good engine will be referred to by the term “healthy turboshaft engine”.
The technical problem is thus posed of minimising the period which separates the detection of the sudden loss of power of the inoperative turboshaft engine and achieving maximum power in the emergency regime of the healthy turboshaft engine.
The shorter this period, the safer the flight is. Furthermore, the shorter this period, the more the helicopter can have a significant take-off mass. Minimising the period which separates the detection of the loss of power of the inoperative engine from achieving the full power of the healthy engine is thus beneficial in two ways.
Nowadays, it is known to detect the loss of power of the inoperative engine by comparing the operating regimes of the two turboshaft engines. If a predetermined difference between the two operating regimes is detected, the turboshaft engine having the worse regime is declared to be inoperative. This loss of power is detected by the identification of a difference between the speeds of the gas turbines which is greater than a predetermined threshold or a difference between the torques of the two engines which is greater than a predetermined threshold.
Once the loss of power is detected, the healthy engine is controlled in order to reach the maximum regime thereof in the emergency regime, which consists in increasing the maximum torque and speed stops of the gas turbine to the maximum permissible stops. Subsequently, the fall in the rotational speed of the rotary wing of the helicopter following the loss of the inoperative engine will lead, by means of the regulation of the speed of the rotary wing by the healthy engine, to an increase in the setpoint value of the fuel flow rate.
The technical problem is posed of providing a better solution to further minimise the period which separates the detection of the sudden loss of power of the inoperative turboshaft engine and achieving maximum power in the emergency regime of the healthy turboshaft engine.